1. Technical Field
The present disclosure relates to a vehicle exterior environment recognition device that recognizes content of a traffic sign that is confirmed outside a vehicle.
2. Related Art
Conventionally, there are techniques to detect a particular object, such as another vehicle located ahead of a vehicle (for example, see Japanese Patent No. 3349060B). Such a technique is used to avoid a collision with a leading vehicle (collision avoidance control), or to control a distance between the two vehicles to be maintained at a safe distance (cruise control). In order to reduce accidents resulting from speeding, demands for techniques to recognize a speed limit provided for each road and control the speed of the vehicle is increasing.
In order to safely travel the vehicle within a speed limit, it is necessary to recognize content of a traffic sign located at a road shoulder or a gate, and to correctly grasp the speed limit of the currently traveling road. For example, Japanese Unexamined Patent Application Publication (JP-A) No. 2012-243051 discloses a technique to apply Hough transform to part corresponding to an edge on a screen image, and recognize an image of a circular traffic sign (hereinafter, an image of the traffic sign is also simply referred to as “the traffic sign”). In this technique, a processing load required for the Hough transform is reduced, whereby the efficiency of identifying the traffic sign can be improved.
In order to perform the Hough transform and to recognize the circular traffic sign, a feature point corresponding to part of the circumference of the circular traffic sign is first identified, points on the circumference that are separated from the feature point by a predetermined distance are voted, and a candidate of the traffic sign having a center position and a radius of the circle is identified according to the number of votes obtained. Then, the content of the traffic sign is recognized by applying, for example, pattern matching, to the candidate of the traffic sign. However, the traffic signs that present a speed limit may be different in the size and/or the shape of numerals indicating the speed limits, and/or in the distance between the numerals, in each country. Therefore, if the pattern matching is simply performed disregarding the differences, the matching may be established for the content that should not be originally matched, whereby troubles may be caused in the safe traveling.